In its 2006 Report of the Committee on the Future of Emergency Care in the United States Health System, the IOM bluntly declared that there is a national epidemic of overcrowded EDs [Emergency Departments] and trauma centers. In simple economic terms, a critical imbalance exists between supply and demand. Unfortunately, little population-based research exists that focuses on demand factors for individual ED visits, and no studies have been published on demand factors for ED use patterns over time. We propose to develop one or more typologies that reflect an older adults pattern of ED use over time (as opposed to focusing on single ED visits) among a nationally representative sample of Medicare beneficiaries (Specific Aim 1), and to examine the antecedents (Specific Aim 2) and consequences (Specific Aim 3) of these ED use patterns. We focus on older adults because in 2003 Medicare paid for 16% of the 114 million ED visits, providing it with a monopsonistic ability to intervene via payment policy. We will link data from four sources. The first is the 1993 baseline and 1995, 1998, 2000, 2002, and 2004 follow-up interviews with the 7,447 non-institutionalized individuals who participated in the Study of Assets and Health Dynamics Among the Oldest Old (AHEAD). These subjects were born before 1924 and were 70 years old or older at baseline. The second data source is the National Death Index (NDI), which contains vital status information on the AHEAD subjects through December 31, 2004. The third data source is the geocode identifiers for the AHEAD subjects at each wave of data collection. The final data source is the Medicare Part A and B claims for the AHEAD subjects that will be available for calendar years 1989 through 2004. The typologies for Specific Aim 1 will be developed based on CPT relative intensity codes and ICD9-CM diagnostic codes, as well as their relationship to criterion validity measures, such as hospital admission rates, arrival by ambulance, proportional share of all health care received in the ED, and mortality. Specific Aim 2 will be evaluated focusing first on individual ED visits using hierarchical (three levels: ED visits, subject, county) generalized linear modeling. Although a comprehensive set of covariates will be included, we are especially interested in education, the characteristics of the local health care delivery system, and continuity of care. We will then focus on modeling ED use patterns using similar two-level (person and county) models. In Specific Aim 3 the appropriate two-level, multivariable statistical models (Cox frailty regression for the time to the first dated event like hospitalization for ACSCs or mortality, binomial regression for constrained-range count variables like the number of hospital episodes, and Poisson regression for skewed extended-range variables like physician visits and total charges), will first estimate the crude effects of the given set of ED use pattern dummy variables, and then decompose these effects by sequentially introducing standard covariates. In its 2006 Report of the Committee on the Future of Emergency Care in the United States Health System, the IOM bluntly declared that there is a national epidemic of overcrowded EDs [Emergency Departments] and trauma centers. Unfortunately, little population-based research exists that focuses on demand factors for individual ED visits, and no studies have been published on demand factors for ED use patterns over time. We propose to develop one or more typologies that reflect an older adults pattern of ED use over time (as opposed to focusing on single ED visits) among a nationally representative sample of Medicare beneficiaries (Specific Aim 1), and to examine the antecedents (Specific Aim 2) and consequences (Specific Aim 3) of these ED use patterns.